An interface unit such as a peripheral component interconnect (PCI) Express interface unit may comprise a transmitter, a receiver, and a compensation unit. The transmitter may comprise a driver circuit in pull-down configuration and the driver circuit may require accurate voltage level such as (Vsupply−0.5) volts. The compensation unit may comprise a dummy driver and a voltage reference generator. The voltage reference generator may comprise voltage addition circuits. The dummy driver may comprise H-bridge circuit, which may be similar to the driver circuit of the transmitter unit. The compensation unit may compare the voltages generated by the voltage reference generator and the dummy driver before generating a correction signal, which may be used to generate accurate voltage levels such as (Vsupply−0.5) volts.